Direct Observation of 2D Electrostatics and Ohmic Contacts in 2D Heterojunctions

 · Invited

Abstract

Atomically thin semiconductors such as WS2, MoS2, WSe2 and MoSe2 are attractive candidates for making ultrathin field effect transistors and optoelectronics. However, owing to the saturated bonds of van der Waals surface, achieving Ohmic contacts which can largely improve their device performance is challenging. Here we introduce a way to prepare large-area graphene contacts to WS2 using seedless chemical vapour deposition. The template-grown graphene/WS2 heterojunctions are intriguing blocks for making WS2 devices with Ohmic contacts. Kelvin probe force microscopy, photoluminescence spectroscopy, and scanning tunneling microscopy characterize the doping and electrostatics in graphene–WS2 heterojunctions as-grown on sapphire and transferred to SiO2 with and without thermal annealing. Both p–n and n–n junctions are observed, and a flat-band condition (zero Schottky barrier height) is found, promising low-resistance Ohmic contacts. This indicates a more favorable band alignment for graphene–WS2 than has been predicted, likely explaining the low barriers observed in transport experiments on similar heterojunctions. Electrostatic measurement and modelling demonstrate that the large depletion width of the graphene–WS2 junction reflects the electrostatics of the one-dimensional junction between two-dimensional materials.

*C.Z. acknowledges support from ARC DECRA (DE140101555).

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Presenters

  • Changxi Zheng

    • Monash Center for Atomically Thin Materials, Monash University

Authors

  • Changxi Zheng

    • Monash Center for Atomically Thin Materials, Monash University

  • Qianhui Zhang

    • Department of Civil Engineering, Monash University

  • Bent Weber

    • CQC2T, Univ of New South Wales
    • School of Physics and Astronomy, Monash University

  • HESAMEDDIN ILATIKHAMENEH

    • Network for Computational Nanotechnology, Purdue University

  • Fan Chen

    • Network for Computational Nanotechnology, Purdue University

  • Harshad Sahasrabudhe

    • Network for Computational Nanotechnology, Purdue University

  • Rajib Rahman

    • Network for Computational Nanotechnology, Purdue University

  • Shiqiang Li

    • Department of Electrical and Electronic Engineering, University of Melbourne

  • Zhen Chen

    • School of Physics and Astronomy, Monash University

  • John Hellerstedt

    • Department of Physics and Astronomy and Centre for Future Low Energy Electronics Technologies, Monash University
    • School of Physics and Astronomy, Monash University
    • Czech Academy of Sciences Institute of Physics

  • Yupeng Zhang

    • Department of Materials Science and Engineering, Monash University

  • Wenhui Duan

    • Department of Civil Engineering, Monash University

  • Qiaoliang Bao

    • Department of Materials Science and Engineering, Monash University

  • Michael Fuhrer

    • Department of Physics and Astronomy and Centre for Future Low Energy Electronics Technologies, Monash University
    • ARC Centre of Excellence in Future Low-Energy Electronics Technologies (fleet.org.au), Monash University
    • Monash Center for Atomically Thin Materials, Monash University